The present invention relates to a sealing arrangement for the sealed leadthrough of rotating shafts through bore holes in housings, comprising at least one lip seal with a sealing lip.
Lip seals are used in many applications in which rotating shafts are run in a sealed arrangement into or out of housings, for example at propeller drive shafts in boat engines, as disclosed in EP 335 368 A1. Here, as in the sealing ring according to EP 1 055 849 A2, the sealing lip faces the area that is normally under lower pressure. In the latter case, measures are implemented to maintain the same pressure on both sides of the sealing lip, however this pressure maintained at a constant level. Lip seals are also known, for example from DE 40 39 666 A1, that are not under pressure at all.
Further, EP 0 480 693 A1 describes a shaft sealing arrangement between chambers with different pressures, for example in pumps or turbines, where mixing of the fluids on either side should be avoided. This is achieved by a fluid with a higher pressure being fed into the seal, which then exits on either side of it. Devices of this kind cannot be used, however, if an absolute seal is to be created in at least one direction, for example towards the atmosphere.
Very simple and low-cost lip seals for sealing shafts are also used in the paper industry for small refiners, however the sealing lip here usually faces the area under higher pressure in order to prevent the medium from escaping from the refiner. Inside these devices for shredding wood chips in the process for making paper pulp there are larger and smaller fluctuations in pressure. Since, however, lip seals are sensitive to higher fluctuations in pressure and can easily start to leak, they can only be used at low pressures or low pressure fluctuations. In the case of refiners, the ratio between inside and outside pressure lies between approximately 1.2 and 1.5 to 1.
A further application, which requires however at least two lip seals mounted in series, is described in DE 10 2005 019 654 A1. Here, a pressurizing means is pressed into the space between the lip seals, however no indication can be found of how this pressure is maintained or how constant it is, which is also due to this state of the art concentrating entirely on sealing problems as a result of contaminants on the lip seals. On the other hand, the lip seal closest to the inside of the housing is—only as an additional measure—flushed with very large quantities of pressurizing means that flow into the inside of the housing with little throttling in order to remove contaminants from the area of the lip sealing arrangement.
In large refiners with higher pressures and generally when larger pressure fluctuations occur, axial face seals are used. Axial face seals are very expensive, as well as being brittle due to the hard-hard combination, and can break at high pressure peaks, meaning that the plant must be shut down immediately. A further method of sealing to be mentioned is the stuffing box, which has also been known for a long time. The disadvantage of stuffing boxes is that they always have some leakage, they are difficult to adjust in order to obtain a good compromise between sealing and leakage, as well as not too much resistance to rotation by the shaft—which is needed however to lubricate and cool the seals.